Etching of plastic using acidic solutions containing trivalent manganese

ABSTRACT

A method of preparing a solution capable of etching a platable plastic. The method comprises the steps of: (a) providing an electrolyte comprising a solution of manganese(II) in a solution of 9 to 15 molar sulfuric acid or phosphoric acid to an electrolytic cell; (b) applying a current to the electrolytic cell, wherein the electrolytic cell comprises an anode and a cathode; and (c) oxidizing the electrolyte to form manganese(III) ions, wherein the manganese(III) ions form a metastable sulfate complex. Thereafter, a platable plastic may be immersed in the metastable sulfate complex for a period of time to etch the platable substrate prior to subsequent plating steps.

FIELD OF THE INVENTION

The present invention relates generally to methods of preparing plasticsfor subsequent plating thereon.

BACKGROUND OF THE INVENTION

It is well known in the art to plate non-conductive substrates, (i.e.plastics) with metal for a variety of purposes. Plastic moldings arerelatively inexpensive to produce and metal plated plastic is used formany applications. For example, metal plated plastics are used fordecoration and for the fabrication of electronic devices. An example ofa decorative use includes automobile parts such as trim. Examples ofelectronic uses include printed circuits, wherein metal plated in aselective pattern comprises the conductors of the printed circuit board,and metal plated plastics used for EMI shielding. ABS resins are themost commonly plated plastics for decorative purposes while phenolic andepoxy resins are the most commonly plated plastics for the fabricationof printed circuit boards.

Preparing plastics for subsequent plating is a multistep process andtypical process steps

-   -   1) etching the substrate with a chromic acid etching solution;    -   2) neutralizing the etched surface with a chrome neutralizing        solution;    -   3) activating the etched surface using a colloidal palladium tin        activator;    -   4) removing tin with an accelerating step; and    -   5) depositing a layer of electroless copper or electroless        nickel followed by electrolytic copper and/or nickel plating.

The initial etching of the plastic substrates is an essential part ofthe overall process, and essentially all commercial processes haveutilized a chromic acid etch solution as a source of hexavalent chromiumfor the plastic etching step. This process has many attributes. Variousplastics including ABS and ABS/polycarbonate blends can be plated withgood plate appearance and adhesion. Immersion time and/or temperature inthe chromic acid etch solution can be increased to plate more difficultplastics containing higher levels of polycarbonate or polypropylene.Extremely difficult plastics that are etch resistant, such as purepolycarbonate, can also be plated by incorporating a solvent prior tothe chromium etching step.

Only certain types of plastic components are suitable for plating, and,as discussed above, the most common types of plastic for electroplatingare acrylonitrile/butadiene/styrene (ABS) or a blend of this materialwith polycarbonate (ABS/PC). ABS consists of two phases.

There is a relatively hard phase consisting of an acrylonitrile/styrenecopolymer and a softer polybutadiene phase. Currently, this material isetched almost exclusively using a mixture of chromic and sulfuric acids.This oxidizing acid mixture is highly effective as an etchant for ABSand ABS/PC. The polybutadiene phase of the plastic contains double bondsin the polymer backbone and these are oxidized by the chromic acid thuscausing complete breakdown and dissolution of the polybutadiene phaseexposed at the surface of the plastic thus giving an effective etch tothe surface of the plastic.

The purpose of the etching step is two fold. First, the plastic isetched to increase surface area. Secondly, the plastic is madehydrophilic, making the surface receptive to subsequent activating andplating stages. Typical chromic acid etching solutions are described,for example, in U.S. Pat. No. 4,610,895 to Tubergen et al., U.S. Pat.No. 6,645,557 to Joshi and U.S. Pat. No. 3,445,350 to Klinger et al.,which are herein incorporated by reference in their entirety.

One problem with the traditional chromic acid etching step is thatchromic acid is a recognized carcinogen and is increasingly regulated,insisting that wherever possible, the use of chromic acid is replacedwith safer alternatives. The use of a chromic acid etchant also haswell-known and serious drawbacks, including the toxicity of chromiumcompounds which makes their disposal difficult, chromic acid residuesremaining on the polymer surface that inhibit electroless deposition,and the difficulty of rinsing chromic acid residues from the polymersurface following treatment. Additionally, hot hexavalent chromiumsulfuric acid solutions are naturally hazardous to workers. Burns andupper respiratory bleeding are common in workers routinely involved withthese chrome etch solutions. Thus, it is very desirable that saferalternatives to acidic chromium etching solutions be developed.

Permanganate solutions are described in U.S. Pat. No. 3,625,758 to Stahlet al., which is herein incorporated by reference in its entirety. Stahlsuggests the suitability of either a chrome and sulfuric acid bath or apermanganate solution for preparing the surface.

U.S. Pat. No. 4,948,630 to Courduvelis et al., which is hereinincorporated by reference in its entirety, describes a hot alkalinepermanganate solution that also contains a material, such as sodiumhypochlorite, that has an. oxidation potential higher than the oxidationpotential of the permanganate solution and is capable of oxidizingmanganate ions to permanganate ions. U.S. Pat. No. 5,648,125 to Cane,which is herein incorporated by reference in its entirety, describes theuse of an alkaline permanganate solution comprising potassiumpermanganate and sodium hydroxide, wherein the permanganate solution ismaintained at an elevated temperature, i.e., between about 165° F. and200° F. U.S. Pat. No. 4,042,729 to Polichette et al., which is hereinincorporated by reference in its entirety describes an etching solutionthat comprises water, permanganate ion, and manganate ion, wherein themolar ratio of manganate ion to permanganate ion is controlled and thepH of the solution is maintained at 11-13.

U.S. Pat. No. 5,229,169 to Chao, which is herein incorporated byreference in its entirety, describes a process for depositing a metallayer on the surface of a polycarbonate-ABS resin (or other similarresin) comprising the steps of contacting the surface with an aqueousmetal hydroxide solution, contacting the surface with an aqueousalkaline solution of a water-soluble permanganate, removing any residueof manganese compounds by contact with a reducing agent, and depositingan electroless metal layer on the surface. The alkaline permanganategenerally comprises sodium or potassium permanganate and the reducingagent may comprise, for example, a solution of hydroxylamine salts.

However, attempts to use permanganate for etching plastics (other thanepoxy base printed circuit boards) have not had much success. First, thesurface treatment of the plastic is inconsistent, sometimes yieldinggood adhesion and sometimes yielding poor adhesion under identicaltreatment conditions. Second, permanganate solutions can be unstable,have a short life and are rapidly decomposed to manganese dioxide.Furthermore, as compared to chrome etchants, permanganate is lesseffective and not suitable for the wide range of plastic mixtures platedin general metal finishing operations.

None of these attempts to etch plastic using permanganate ions have beencapable of producing etch characteristics which match those obtained bythe use of chromic acid and the stability of the etching solutions isalso poor, resulting in the formation of manganese dioxide sludge.

Other attempts to replace the chrome etching are also described in theprior art. For example, U.S. Pat. Nos. 4,941,940, 5,015,329, and5,049,230, all to Patel et al., which are herein incorporated byreference in their entirety, describe a single or multi-step process forpre-swelling and etching of functionalized polymers, such aspolycarbonates, using an etching solution that comprises at least oneswelling agent and at least one degradation agent. The preparedsubstrates are then plated with electroless nickel or electrolesscopper.

U.S. Pat. No. 5,160,600 to Patel et al., which is herein incorporated byreference in its entirety, replaces the chromic acid etching solutionwith an etching solution that comprises sulfuric acid, and optionallyphosphoric acid and/or nitric acid. The treated substrate is thenimmersed in an aqueous suspension of palladium.

Regardless of whether the oxidant solution is a hexavalent chromiumsolution or a permanganate solution, contact with the solution leaves anoxidant residue on the surface of the plastic part that acts to poisonthe catalytic surface, interfering with metal deposition and oftenresulting in void formation. A simple water rinse is generallyinadequate to remove the residue and the art has thus resorted to afurther step of contact with a solution of a reducing agent althoughmore chemistry is involved in removal of oxidant residue than simplereduction. Removal of permanganate residue with a reducing agent isdisclosed in above referenced U.S. Pat. No. 4,610,895 to Tubergen andU.S. Pat. No. 6,645,557 to Joshi.

As is readily seen, many etching solutions have been suggested as areplacement for chromic acid in processes for preparing non-conductivesubstrates for metallization. However, none of these processes haveproven satisfactory for various economic, performance and/orenvironmental reasons and thus none of these processes have achievedcommercial success or been accepted by the industry as a suitablereplacement for chromic acid etching.

The tendency for permanganate based solutions to form sludge and undergoself-decomposition has been noted. Under strongly acidic conditions,permanganate ions can react with hydrogen ions to produce manganese (II)ions and water according to the following reaction:4MnO₄ ⁻+12-H⁺→4Mn²⁺+6H₂O+5O₂  (1)

The manganese (II) ions formed by this reaction can then undergo furtherreaction with permanganate ions forming a sludge of manganese dioxideaccording to the following reaction:2MnO₄ ⁻2H₂O+3Mn²⁺→5MnO₂+4H⁺  (2)

Thus formulations based on strongly acidic permanganate solutions areintrinsically unstable irrespective of whether the permanganate ion isadded by alkali metal salts of permanganate or is electrochemicallygenerated in situ. In comparison to the currently used chromic acidetches, the poor chemical stability of acidic permanganate renders iteffectively useless for large scale commercial application. Alkalinepermanganate etches are more stable, and are widely used in the printedcircuit board industry for etching epoxy based printed circuit boards,but alkaline permanganate is not an effective etchant for plastics suchas ABS or ABS/PC. Thus, manganese (VII) is unlikely to gain widespreadcommercial acceptance as an etchant for these materials.

Other attempts to etch ABS without the use of chromic acid have includedthe use of electrochemically generated silver (II) or cobalt (III). Formany years, it has been known that certain metals can be anodicallyoxidized to oxidation states which are highly oxidizing. For example,manganese (II) can be oxidized to permanganate (manganese VI), cobaltcan be oxidized from cobalt (II) to cobalt (III) and silver can beoxidized from silver (I) to silver (II).

There is currently no suitable commercially successful etchant forplastics based on either permanganate (in either acid or alkaline form),on manganese in any other oxidation state or by using other acids oroxidants.

Thus, there remains a need in the art for an improved etchant forpreparing plastic substrates for subsequent electroplating that does notcontain chromic acid and that is commercially acceptable.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an etchant for plasticsubstrates that does not contain chromic acid.

It is another object of the present invention to an etchant for plasticsubstrates that is commercially acceptable.

It is still another object of the present invention to provide anetchant for plastic substrates that is based on manganese ions.

The present invention relates generally to a composition suitable forthe etching of ABS, ABS/PC and other plastic materials and a method ofusing the same.

In one embodiment, the present invention relates generally to a methodof preparing a solution capable of etching a plastic substrate, themethod comprising the steps of:

providing an electrolyte comprising a solution of manganese(II) in asolution of 9 to 15 molar sulfuric acid or phosphoric acid to anelectrolytic cell;

applying a current to the electrolytic cell, wherein the electrolyticcell comprises an anode and a cathode;

oxidizing the electrolyte to form manganese(III) ions, wherein themanganese(III) ions form a metastable sulfate complex; and

treating the plastic substrate in the electrolyte.

In another embodiment, the present invention relates generally to anelectrolyte capable of etching a plastic substrate, the electrolytecomprising a solution of manganese(III) in a solution of 9 to 15 molarsulfuric acid or phosphoric acid.

In one preferred embodiment, the electrolyte composition may be used toetch ABS or ABS/PC at a temperature of between 30 to 80° C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventors of the present invention have found that trivalentmanganese can readily he produced by electrolysis at low current densityof divalent manganese ions in strong sulfuric acid, More particularly,the inventors of the present invention have discovered that a solutionof trivalent manganese ions in strongly acidic solution is capable ofetching ABS.

Trivalent manganese is unstable and is highly oxidizing (standard redoxpotential of 1.51 versus normal hydrogen electrode). In solution, itvery rapidly disproportionates to manganese dioxide and divalentmanganese via the following reaction:2Mn³⁺+2H₂O→MnO₂+Mn²⁺+4H+  (3)

However, in a strong sulfuric acid solution, the trivalent manganese ionbecomes meta-stable and forms a cherry purple/red colored sulfatecomplex. The inventors have found that this sulfate complex is asuitable medium for the etching of ABS and has many advantages overchromium-free etches previously described.

In one embodiment, the present invention relates generally to a methodof preparing a solution capable of etching a plastic substrate, themethod comprising the steps of;

providing an electrolyte comprising manganese(II) ions in a solution of9 to 15 molar sulfuric acid or phosphoric acid to an electrolytic cell;

applying a current to the electrolytic cell, wherein the electrolyticcell comprises an anode and a cathode;

oxidizing the electrolyte to form manganese(III) ions, wherein themanganese(III) ions form a metastable sulfate complex; and

treating the plastic substrate with the electrolyte to etch the surfaceof the plastic substrate.

In a preferred embodiment, the plastic substrate comprises ABS orABS/PC.

While it is contemplated that both phosphoric acid and sulfuric acidwould work in compositions of the present invention, in a preferredembodiment, the acid is sulfuric acid. The stability of manganese (III)ions in sulfuric and phosphoric acids has been studied. At ambienttemperatures, the half life of the manganese (III) ions in 7M sulfuricacid is on of the order of 2 years. By comparison, the half life ofsimilar concentrations of manganese (III) ions in 7M phosphoric acid wasaround 12 days. It is suggested that the much higher stability of themanganese (III) ions in sulfuric acid is due to the formation ofmangano-sulfate complexes and the higher concentration of availablehydrogen ion concentration in the sulfuric acid solution. A furtherproblem with the use of phosphoric acid is the limited solubility ofmanganese (III) phosphate. Thus, although other inorganic acids such asphosphoric acid can be usable in the compositions of the presentinvention, it is generally preferred to use sulfuric acid.

The remarkable stability of manganese (III) ions in strong sulfuric acidprovides the following advantages in use:

-   -   1) Because the Mn(III) ions are formed at a low current density,        the power requirements for the process are typically very low.    -   2) Because the anode operates at a very low current density, a        small cathode in relationship to the anode area can be used to        prevent cathodic reduction of the Mn(III) ions. This obviates        the need for a divided cell and makes the engineering of an        etchant regeneration cell simpler.    -   3) Because the process does not produce permanganate ions, there        is no possibility of producing manganese heptoxide in the        solution (this is a considerable safety hazard as it is        violently explosive).    -   4) Because of the high stability of the Mn(III) ions in strong        sulfuric acid, the etchant can be sold ready for use. In        production, the etchant requires only a small regeneration cell        at the side of the tank in order to maintain the Mn(III) content        of the etch and prevent the build-up of Mn(II) ions.    -   5) Because other etch processes are based on permanganate, the        result of the reaction of permanganate with Mn(II) ions causes        rapid “sludging” with manganese dioxide and a very short        lifetime of the etch. This should not be an issue with the        Mn(II) based etch (although there may be some disproportionation        over time).    -   6) The electrolytic production of Mn(III) in accordance with the        present invention does not produce any toxic gases. Some        hydrogen may be produced at the cathode, but owing to the low        current requirements, this would be less than that produced by        many plating processes.

As described herein, in a preferred embodiment the acid is sulfuricacid. The concentration of sulfuric acid may be between about 9 andabout 15 molar. The concentration of sulfuric acid is important in theprocess. Below a concentration of about 9 molar, the rate of etchbecomes too slow to be of use and above about 14 molar, the solubilityof manganese ions in the solution becomes too low to get a usefulconcentration of the manganese into solution. Additionally, very highconcentrations of sulfuric acid tend to absorb moisture from the air andare hazardous to handle. Thus, in a preferred embodiment, theconcentration of sulfuric acid is between about 12 and 13 molar. Thisconcentration of sulfuric acid is dilute enough to allow the safeaddition of water to the etch and strong enough to optimize the etchrate of the plastic. At this concentration of sulfuric acid, up toaround 0.08M of manganese sulfate can be dissolved at the preferredoperating temperature of the etch, For optimal etching, theconcentration of manganese ions in solution should be as high as it isfeasible to achieve.

The manganese(II) ions are preferably selected from the group consistingof manganese sulfate, manganese carbonate and manganese hydroxidealthough other similar sources of manganese(II) ions known in the artwould also be usable in the practice of the invention. The concentrationof manganese(II) ions may be in the range of between about 0.005 molarand saturation. In one embodiment, the electrolyte also comprisescolloidal manganese dioxide. This may form to some extent as a naturalresult of disproportionation of manganese (III) in solution, or may beadded deliberately. Methods of preparing colloidal manganese dioxide arewell known in the art.

Manganese (III) ions can be conveniently generated by electrochemicalmeans by the oxidation of manganese (II) ions. The methodology forefficient production of trivalent manganese ions was determined and itwas found that with the use of a platinum or platinized titanium anode,manganese (II) could be efficiently oxidized to manganese (III) at acurrent density of between 0.1 and 0.4 A/dm². At these currentdensities, the inventors of the present invention have found that theconversion efficiency of manganese (II) under these circumstancesapproaches 100%. Furthermore, at a current density of between 0.1 and0.4 A/dm² using a platinized titanium anode, the anode potential isbelow the oxygen discharge potential and manganese (III) ions areproduced with high efficiency. The inventors have found that etching ofABS can be achieved by this method.

The electrodes may comprise a material selected from the groupconsisting of platinum, platinized titanium, iridium oxide coatedtitanium, niobium and other suitable materials. The cathode may also bemade of platinum, platinized titanium, niobium, iridium oxide coatedtitanium or any other suitable material and is preferably platinum orplatinized titanium. The anode may be made of platinized titanium,platinum, iridium/tantalum oxide, niobium, or any other suitablematerial and is preferably platinum or platinized titanium. Forefficient generation of manganese (III) ions, it is generally necessaryto use an anode area which is large in comparison to the area of thecathode. Preferably, the area ratio of anode to cathode is at leastabout 10:1. By this means, the cathode can be immersed directly in theelectrolyte and it is not necessary to have a divided cell (although theprocess would work with a divided cell arrangement, this would introduceunnecessary complexity and expense).

In addition, it is generally preferable that the electrolyte not containany permanganate ions.

In another embodiment the present invention comprises immersing theplatable plastic in the metastable sulfate complex for a period of timeto etch the surface of the platable plastic. In one embodiment, theplatable plastic is immersed in the solution at a temperature of between30 and 80° C. The rate of etching increases with temperature and is veryslow below 50° C. The upper limit of temperature is determined by thenature of the plastic being etched. ABS begins to distort above 70° C.,thus in a preferred embodiment the temperature of the electrolyte ismaintained between about 50 and about 70° C., especially when etchingABS materials. The time period of the immersion of the plastic in theelectrolyte is preferably between about 20 to about 30 minutes.

Articles etched in this manner may be subsequently electroplated usingconventional pretreatment for plated plastics or the etched surface ofthe plastic could be used to enhance the adhesion of paint, lacquers orother surface coatings.

As described in the examples that follow, the inventors of the presentinvention have determined by means of cyclic voltammetry that at theconcentration of manganese (II) ions used in the etch of this invention,the oxidation is diffusion controlled so efficient agitation of the etchsolution is necessary during the electrolytic oxidation process.

In another embodiment, the present invention relates generally to anelectrolyte capable of etching a platable plastic, the electrolytecomprising a solution of manganese(II) in a solution of 9 to 15 molarsulfuric acid or phosphoric acid. The electrolyte oxidizes to formmanganese(III) ions, wherein the manganese(III) ions form a metastablesulfate complex where sulfuric acid is used.

The invention will now be illustrated with the following non-limitingexamples.

COMPARATIVE EXAMPLE 1

A solution of 0.08 molar of manganese sulfate in12.5 molar sulfuric acid(500 ml) was heated to 70° C. and a piece of platable grade ABS wasimmersed in the solution. Even after an hour immersed in this solution,there was no discernible etching of the test panel and upon rinsing, thesurface was not “wetted” and would not support an unbroken film ofwater.

EXAMPLE 1

The solution of Comparative Example 1 was electrolyzed by immersing aplatinized titanium anode of an area of 1 dm² and a platinized titaniumcathode of surface area 0.01 dm² in the solution and applying a currentof 200 mA for 5 hours.

During this period of electrolysis, the solution was observed to changein color from almost colorless to a very deep purple/red color. It wasconfirmed that no permanganate ions were present.

This solution was then heated to 70° C. and a piece of platable gradeABS was immersed in the solution. After 10 minutes of immersion, thetest piece was fully wetted and would support an unbroken film of waterafter rinsing. After 20 minutes of immersion, the sample was rinsed inwater, dried and examined using a scanning electron microscope (SEM).This examination revealed that the test piece was substantially etchedand many etch pits were visible.

EXAMPLE 2

A test piece of platable grade ABS was etched in a solution prepared asin Example 1 for 30 minutes at 70° C. The sample was then rinsed andplated using the following pretreatment sequence:

-   -   1) Treatment in a proprietary preparation for plating on plastic        (M-neutralize, available from MacDermid, Inc)    -   2) Rinse    -   3) Pre-dip in 30% hydrochloric acid    -   4) Activate in a proprietary palladium colloid activator (D34 C,        available from MacDermid, Inc.)    -   5) Rinse    -   6) Accelerate in a proprietary preparation (Macuplex Ultracel        9369, available from MacDermid, Inc.)    -   7) Rinse    -   8) Plate in electroless nickel process (Macuplex J64, available        from MacDermid, Inc.)    -   9) Rinse    -   10) Plate in acid copper process to a thickness of 30 microns        (CuMac Optima, available from MacDermid)

In all cases, the process parameters were as recommended on thetechnical data sheet for each product.

After the copper plating process was completed, the sample was dried andexamined. The copper deposit was bright and clear with no evidence ofblistering and showed good adhesion of the deposit to the substrate.

EXAMPLE 3

A solution containing 12.5 M of sulfuric acid and 0.08 M manganese (IDsulfate was electrolyzed using a platinized titanium anode at a currentdensity of 0.2 A/dm². A platinized titanium cathode having an area ofless than 1% of the anode area was used in order to prevent cathodicreduction of the Mn(III) ions produced at the anode. The electrolysiswas performed for long enough for sufficient coulombs to be passed tooxidize all of the manganese (II) ions to manganese (III). The resultingsolution was a deep cherry purple/red color. There were no permanganateions generated during this step. This was also confirmed by visiblespectroscopy—the Mn(III) ions produced a completely different absorptionspectrum from that of a solution of permanganate.

EXAMPLE 4

The etching solution prepared as described above in Example 3 was heatedto 65-70° C. on a magnetic stirrer/hotplate and test coupons of ABS wereimmersed in the solution for time periods of 20 and 30 minutes. Some ofthese test coupons were examined by SEM and some were processed in anormal plating on plastic pretreatment sequence (reduction inM-neutralize, predip, activate, accelerate, electroless nickel, copperplate to 25-30 microns). These test coupons were then annealed andsubjected to peel strength testing using an Instron machine.

Peel strength testing carried out on coupons plated for 30 minutesdemonstrated peel strength varying between about 1.5 and 4 N/cm.

Cyclic voltammograms were obtained from a solution containing 12.5Msulfuric acid and 0.08M manganese sulfate using a platinum rotating diskelectrode (RDE) having a surface area of 0.196 cm² at various rotationspeeds. A model 263A potentiostat and a silver/silver chloride referenceelectrode were used in conjunction with the RDE.

In all cases, the forward scan showed a peak at around 1.6V vs. Ag/AgClfollowed by a plateau up to around 1.75V followed by and increase incurrent. The reverse scan produced a similar plateau (at a slightlylower current and a peak around 1.52V. The dependence of these resultson the rate of electrode rotation indicates mass transport control is aprimary factor in the mechanism. The plateau indicates the potentialrange over which Mn(III) ions are formed by electrochemical oxidation.

A potentiostatic scan was performed at 1.7V. It was observed that thecurrent initially dropped and then over a period of time increased. Thecurrent density at this potential varied between 0.15 and 0.4 A/dm².

Following this experiment, a galvanostatic measurement was taken at aconstant current density of 0.3 A/dm². Initially, the applied currentdensity was achieved by a potential of about 1.5V but as the experimentprogressed, after about 2400 seconds, and increase in potential to about1.75V was observed.

The results of these experiments demonstrate that manganese (III) ionscan be generated by electrosynthesis at low current densities using aplatinum or platinized titanium anode.

After a period of etching for more than 10 minutes, it was observed thatthe surface of the ABS test coupons was fully wetted and would supportan unbroken film of water alter rinsing. After a period of 20 or 30minutes, the panels were noticeably etched.

What is claimed is:
 1. A method of preparing a solution capable ofetching a platable plastic, the method comprising the steps of:providing an electrolyte comprising manganese(II) ions in a solution ofabout 9 to 15 molar sulfuric acid or phosphoric acid to an electrolyticcell; applying a current to the electrolytic cell, wherein theelectrolytic cell comprises an anode and a cathode; and oxidizing theelectrolyte to form manganese(III) ions, wherein the manganese(III) ionsform a metastable sulfate or phosphate complex, wherein the solutionadditionally comprises colloidal manganese dioxide.
 2. The methodaccording to claim 1, wherein the acid is sulfuric acid.
 3. The methodaccording to claim 2, wherein the sulfuric acid has a concentration of12 to 13 molar.
 4. The method according to claim 1, wherein themanganese(II) ions are selected from the group consisting of manganesesulfate, manganese carbonate and manganese hydroxide.
 5. The methodaccording to claim 1, wherein the concentration of the manganese(II)ions in the electrolyte is between about 0.005 molar and saturation. 6.The method according to claim 1, wherein the cathode comprises amaterial selected from the group consisting of platinum, platinizedtitanium, iridium/tantalum oxide, and niobium.
 7. The method accordingto claim 6, wherein the cathode is platinized titanium or platinum. 8.The method according to claim 1, wherein the area of the anode is largerthan the area of the cathode.
 9. The method according to claim 8,wherein the area ratio of the anode to the cathode is at least about10:1.
 10. The method according to claim 1, wherein the anode currentdensity is between about 0.1 to about 0.4 A/dm².
 11. The methodaccording to claim 1, wherein the temperature of the electrolyte ismaintained between about 30° C. and about 80° C.
 12. The methodaccording to claim 1, wherein the electrolyte does not contain anypermanganate.
 13. A method of preparing a solution capable of etching aplatable plastic, the method comprising the steps of: providing anelectrolyte comprising manganese(II) ions in a solution of about 9 to 15molar sulfuric acid or phosphoric acid to an electrolytic cell; applyinga current to the electrolytic cell, wherein the electrolytic cellcomprises an anode and a cathode; oxidizing the electrolyte to formmanganese(III) ions, wherein the manganese(III) ions form a metastablesulfate or phosphate complex, and immersing the platable plastic in themetastable sulfate complex for a period of time to etch the platablesubstrate; wherein the platable plastic is immersed in the metastablesulfate complex for about 20 to about 30 minutes.
 14. The methodaccording to claim 13, wherein the platable plastic comprisesacrylonitrile-butadiene-styrene oracrylonitrile-butadiene-styrene/polycarbonate.
 15. An electrolytecapable of etching a platable plastic, the electrolyte comprisingmanganese(III) ions in a solution of 9 to 15 molar sulfuric acid orphosphoric acid, wherein the electrolyte additionally comprisescolloidal manganese dioxide.
 16. The electrolyte according to claim 15,wherein the acid is sulfuric acid.
 17. The electrolyte according toclaim 16, wherein the sulfuric acid has a concentration of 12 to 13molar.
 18. The electrolyte according to claim 15, wherein theconcentration of the manganese(III) ions in the electrolyte is betweenabout 0.005 molar and saturation.
 19. The electrolyte according to claim15, wherein the electrolyte does not contain any permanganate.